1. Field of the Invention
The invention relates to methods for deforming an elongated workpiece so as to form an elongated product and, more particularly, to methods and apparatus for extruding one or more elongated workpieces through apertures in one or more dies so as to form one or more elongated products.
2. Description of the Prior Art
In the art of forming elongated products of definite length by extruding elongated workpieces of definite length through suitable dies, it is known to employ hydrostatic extrusion techniques, i.e., to apply sufficient hydrostatic pressure to a billet within a pressure vessel to force the billet to pass through an aperture in a die located at an end of the pressure vessel. Typical pressure vessels include solid bore chambers, i.e., closed, cylindrical pressure chambers, with or without liners. It is difficult, however, to load billets into solid bore chambers, especially billets with coatings, e.g., waxes, which are preferred hydrostatic extrusion media for various reasons, such as are set forth in U.S. Pat. Nos. 3,740,985 and 3,985,011, both issued to F. J. Fuchs, Jr., the former of which has been reissued as U.S. Pat. No. Re. 28,795. Each such billet must, together with its wax coating, occupy the entire volume of the solid bore chamber in the vicinity of the die. The only practical loading technique has involved heating the entire solid bore chamber above the melting point of the wax, and then introducing both molten wax and the billet into the heated chamber. Clearly, this is a slow and laborsome billet loading technique, which is not suited to efficient operation of the extrusion apparatus. Indeed, even if it is desired that hot billets be extruded, such billet loading technique may be considered unduely cumbersome and costly.
Solid bore chambers also are subject to fatigue fractures, e.g., in bore liners, caused by severe hoop stress conditions. The use of hydrostatic pressure jackets has alleviated this problem to some degree. It is still common, however, to experience an unbalanced pressure relationship between the external jacket pressure and the internal bore pressure, with the imbalance increasing axially toward the die, during each operation of a hydrostatic billet extruder with a solid bore chamber.
Typical hydraulic billet extrusion techniques also require pressure containers of high strength steel. Difficulties involved in providing such containers of sufficient size generally render it impractical to build very large billet extruders.
It is known, also, to extrude an elongated workpiece of indefinite length continuously through a die, so as to form an elongated product of indefinite length, by driving a number of trains of gripping members continuously, each about an endless path in a single direction of movement, with adjacent portions of the various endless paths coming together, operatively engaging the surface of the workpiece, and advancing the workpiece continuously toward and through the die. The workpiece may initially be coated with a suitable hydrostatic medium, e.g., a wax, with the apparatus including mechanisms for providing a gradient in pressure, increasing in the direction of the die, for externally supporting the gripping members against increasing pressure in the workpiece and the coating thereon as the coated workpiece is forced continuously into the die by the continuously advancing gripping members. Two examples of such continuous extrusion techniques are provided by the previously mentioned U.S. Pat. Nos. 3,740,985 and 3,985,011, the former of which has been reissued as U.S. Pat. No. Re 28,795.
The techniques and the apparatus disclosed in such previously mentioned patents, while also capable of extruding successions of billets of definite length to form successions of elongated products of definite length where the billets are of small or moderate cross-section, are specifically designed for the continuous extrusion of elongated workpieces of indefinite length to form elongated products of indefinite length. To some extent, various factors, such as maximum cross-sectional area of each elongated workpiece and rapid replaceability of extrusion dies with new dies of similar or differing aperture configurations, may be sacrified in such apparatus in order to permit continuous, high-speed extrusion to occur. Accordingly, it would clearly be advantageous to have at one's disposal methods and apparatus which are particularly suited to overcoming the previously discussed problems in the hydrostatic extrusion of billets of definite length, and which will preferably also permit the rapid and efficient extrusion of a succession of either heated or unheated billets of definite length, which billets may have relatively large cross-sections, with successive extrusions taking place either through the same die to form a succession of like elongated products, or through a plurality of rapidly interchanged dies to form either a succession of like elongated products or a succession of varying elongated products.